Flexible plugging agent for offshore oil and gas drilling fluid and preparation method and application thereof

Abstract

The application provides a flexible plugging agent for offshore oil and gas drilling fluid and a preparation method and application thereof, and belongs to the technical field of offshore oil and gas drilling and production. The plugging agent is prepared from the following raw materials: styrene, N-phenylmaleimide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, 2-methacryloyloxyethylphosphorylcholine, a crosslinking agent, an initiator, a hydrophilic emulsifier, an oleophilic emulsifier and water. The plugging agent has excellent structural stability, heat resistance, salt resistance and hydration stability, has good adaptability to a low-density drilling fluid system, has a flexible deformation capacity, can effectively enter a complex leakage passage to achieve effective plugging, and can maintain the integrity and stability of a plugging layer under drilling fluid circulation shearing, temperature fluctuation and complex downhole conditions, thereby having applicability in a high-temperature and high-pressure drilling environment.

Description

Technical Field

[0001] This invention relates to a flexible plugging agent for marine oil and gas drilling fluid, its preparation method and application, belonging to the field of marine oil and gas drilling and production technology. Background Technology

[0002] As offshore oil and gas exploration and development continues to advance into deepwater and ultra-deepwater areas, drilling fluid systems face multiple challenging conditions during deepwater drilling, including high-salt environments, complex downhole temperature and pressure conditions, narrow safety density windows, and complex leakage pathways. Due to the lower pressure-bearing capacity of deepwater formations and the narrower safety density window of drilling fluids, the conflict between wellbore stability and leakage prevention is particularly pronounced. Simultaneously, the drilling fluid must withstand high temperatures and pressures during wellbore circulation, which can easily lead to increased filtration loss and affect the stability of the plugging layer. Therefore, plugging materials suitable for deepwater drilling should not only possess good fracture penetration and plugging capabilities but also consider compatibility with deepwater drilling fluid systems, low system densification effects, a certain degree of flexible deformation capacity, and stable plugging performance under high temperature and pressure conditions.

[0003] In the prior art, Chinese patent document CN113549437A discloses a method for preparing and applying a self-degradable leak-proof and plugging polymer composite material suitable for deepwater and ultra-deepwater drilling fluids. This material can be used in conjunction with deepwater drilling fluids and emphasizes the automatic degradation and unblocking effect after temporary plugging, as well as the reservoir protection effect. However, its disclosure mainly focuses on self-degradation and flowback performance, with less attention paid to the flexible adaptability of the plugging material in complex leakage channels and the continuous and stable plugging performance under high temperature and high pressure filtration conditions. Chinese patent document CN116262875A discloses a high-efficiency plugging agent for drilling fluids, its preparation method, and its application. This plugging agent mainly relies on modified plant fibers, nano- and micron-sized calcium carbonate, vermiculite, and mica to form a high-strength plugging layer with a temperature resistance of up to 200℃. However, this technology mainly relies on rigid bridging filler materials to form the plugging layer, and does not adequately consider the adaptability to low-density drilling fluid systems in marine oil and gas and the flexible deformation capability in complex leakage channels.

[0004] In summary, existing technologies struggle to simultaneously meet the comprehensive requirements of offshore oil and gas drilling fluid systems for plugging materials, such as compatibility in low-density systems, flexible deformation capabilities, effective entry into complex leakage channels, and stable plugging performance under high temperature and pressure conditions. Therefore, developing a low-density flexible plugging agent suitable for offshore oil and gas drilling conditions is of great significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a flexible plugging agent for marine oil and gas drilling fluids, its preparation method, and its application. The plugging agent of this invention possesses excellent structural stability, thermal stability, salt resistance, and hydration stability. It exhibits good compatibility with low-density drilling fluid systems, possesses flexible deformation capabilities, and can effectively penetrate complex leakage channels to achieve effective plugging. Even under drilling fluid circulation shear, temperature fluctuations, and complex downhole conditions, it can maintain the integrity and stability of the plugging layer, thus demonstrating its applicability in high-temperature and high-pressure drilling environments. When added to drilling fluid, the plugging agent of this invention can form an effective plugging structure at wellbore pores and microfracture entrances, significantly reducing drilling fluid filtration loss and decreasing the equivalent permeability of formation permeability channels, thereby reducing damage to the formation caused by drilling fluid intrusion. Simultaneously, it can weaken pressure transmission to the formation, reduce the probability of fracture propagation and leakage, which is beneficial for maintaining wellbore stability and improving the safety of deepwater drilling operations and the overall performance of the drilling fluid.

[0006] The technical solution of the present invention is as follows:

[0007] A flexible plugging agent for marine oil and gas drilling fluid is prepared from the following raw materials in parts by weight: Styrene 12-16 parts, N-phenylmaleimide 1-4 parts, 2-acrylamido-2-methylpropanesulfonic acid 6-8 parts, sodium p-styrenesulfonate 3-5 parts, 2-methacryloyloxyethyl phosphorylcholine 2-5 parts, crosslinking agent 0.04-0.08 parts, initiator 0.1-0.2 parts, hydrophilic emulsifier 1-3 parts, lipophilic emulsifier 0.2-0.6 parts, water 60-80 parts.

[0008] Preferably, the flexible plugging agent for marine oil and gas drilling fluid is prepared from the following raw materials in parts by weight: 13.5 parts styrene, 2 parts N-phenylmaleimide, 7 parts 2-acrylamido-2-methylpropanesulfonic acid, 4 parts sodium p-styrenesulfonate, 3.5 parts 2-methacryloyloxyethyl phosphorylcholine, 0.06 parts crosslinking agent, 0.12 parts initiator, 2 parts hydrophilic emulsifier, 0.4 parts lipophilic emulsifier, and 70 parts water.

[0009] According to a preferred embodiment of the present invention, the crosslinking agent is N,N′-methylenebisacrylamide.

[0010] According to a preferred embodiment of the present invention, the initiator is potassium persulfate.

[0011] According to the present invention, the hydrophilic emulsifier is octylphenol polyoxyethylene ether (OP-10), and the lipophilic emulsifier is sorbitan monooleate (Span-80).

[0012] The preparation method of the above-mentioned flexible plugging agent for marine oil and gas drilling fluid includes the following steps: (1) Disperse the hydrophilic emulsifier fully in water, add 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, 2-methacryloyloxyethylphosphonic choline, and crosslinking agent, mix thoroughly, adjust pH, and obtain an aqueous phase; (2) Mix the lipophilic emulsifier, styrene, and N-phenylmaleimide evenly to obtain the oil phase; (3) Under stirring conditions, the oil phase is added dropwise to the aqueous phase and emulsified to obtain a pre-emulsion; an initiator aqueous solution is added dropwise, and after polymerization reaction and filtration, a flexible plugging agent for marine oil and gas drilling fluid is obtained.

[0013] According to a preferred embodiment of the present invention, in step (1), the pH is adjusted to 7 using an aqueous sodium hydroxide solution with a mass concentration of 20-40%.

[0014] According to a preferred embodiment of the present invention, in step (3), the emulsification speed is 3000-5000 rpm and the emulsification time is 10-30 min.

[0015] According to a preferred embodiment of the present invention, in step (3), the mass concentration of the initiator aqueous solution is 2%-3%.

[0016] According to a preferred embodiment of the present invention, in step (3), the polymerization reaction temperature is 70-75°C, the polymerization reaction time is 4-6 hours, and the polymerization reaction is carried out under a protective atmosphere and stirring conditions. The protective atmosphere is nitrogen.

[0017] The application of the aforementioned flexible plugging agent in marine oil and gas drilling fluids can effectively reduce drilling fluid loss and form a tight sealing layer in wellbore pores and microfractures, thereby improving wellbore stability and reducing the risk of leakage. Preferably, the mass concentration of the plugging agent in the drilling fluid is 3-4 wt%.

[0018] The technical features and beneficial effects of this invention are as follows:

[0019] 1. This invention utilizes styrene and N-phenylmaleimide copolymerization to construct the polymer backbone. The styrene unit introduces a benzene ring structure, which improves the rigidity of the polymer chain segments. The N-phenylmaleimide molecule contains carbon-carbon double bonds of the maleimide structure, which, under the action of an initiator, can undergo free radical copolymerization with olefin monomers such as styrene and integrate into the polymer backbone; after polymerization, the rigid structure of the imide ring and the N-phenyl substituents are retained. The synergistic effect of the styrene and N-phenylmaleimide structural units improves the thermal and structural stability of the polymer, thereby enabling the resulting plugging agent to maintain good performance stability under high-temperature conditions and contributing to the improvement of the stability of the plugging layer.

[0020] 2. This invention introduces 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate monomers, forming strong sulfonate hydrophilic groups and stable ionic interaction sites in the polymer molecule. This is beneficial for improving the dispersion stability and salt resistance of the material in high-saltification media, and helps reduce the aggregation tendency of polymer particles in salt environments. These structural features make it easier for the plugging agent to form a continuous and dense plugging layer after entering the wellbore pores and microfractures, thereby improving the density and stability of the plugging layer and enhancing the filtration control effect of the drilling fluid.

[0021] 3. This invention introduces a 2-methacryloyloxyethyl phosphorylcholine monomer to construct a phosphorylcholine-type zwitterionic structure in the polymer side chain. This structure exhibits strong hydration ability and interfacial stabilization, which is beneficial for enhancing the continuous dispersion ability of the plugging agent in high-salt, low-temperature aqueous environments and helps improve the stability of the hydration layer on the particle surface. This design makes the plugging agent more suitable for marine oil and gas drilling fluids, maintaining good system compatibility and plugging effect under complex salt environments and low-temperature conditions.

[0022] 4. This invention utilizes a combination of styrene, N-phenylmaleimide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, and 2-methacryloyloxyethylphosphonic choline to create a plugging agent that possesses structural stability, thermal stability, salt resistance, and hydration stability. It exhibits good compatibility with low-density drilling fluid systems, possesses flexible deformation capabilities, and can effectively penetrate complex leakage channels for effective plugging. It maintains the integrity and stability of the plugging layer even under drilling fluid circulation shear, temperature fluctuations (high or low temperature), and complex downhole conditions. It can be used for filtration control in marine oil and gas water-based drilling fluid systems and for plugging wellbore pores and microfractures. The nano-sized emulsion polymer particles of this invention are uniformly dispersed in the system and possess a certain degree of flexibility. After being added to the drilling fluid, they have minimal impact on the original rheological properties of the drilling fluid, such as viscosity and shear stress, and will not cause rheological runaway in low-density drilling fluids. It is not prone to significant aggregation and sedimentation, has little impact on the rheological properties of the system, and can enter complex leakage channels under low solid phase conditions to achieve sealing. Attached Figure Description

[0023] Figure 1 Fourier transform infrared spectrum of the plugging agent for marine oil and gas drilling fluid prepared in Example 1.

[0024] Figure 2 The thermal stability analysis diagram is shown for the plugging agent for marine oil and gas drilling fluid prepared in Example 1.

[0025] Figure 3 The particle size distribution diagram is shown for the plugging agent for marine oil and gas drilling fluid prepared in Example 1.

[0026] Figure 4Photograph of the appearance of the plugging agent for marine oil and gas drilling fluid prepared in Example 1. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0028] Furthermore, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods; and unless otherwise specified, the reagents, materials and equipment are all commercially available.

[0029] Example 1

[0030] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluids includes the following steps:

[0031] (1) Add 2.0 g of octylphenol polyoxyethylene ether (OP-10) to 65.0 g of deionized water and stir at room temperature until completely dissolved; add 7.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 4.0 g of sodium p-styrenesulfonate, 3.5 g of 2-methacryloyloxyethyl phosphorylcholine and 0.06 g of crosslinking agent N,N′-methylenebisacrylamide in sequence, and continue stirring to obtain a homogeneous solution;

[0032] (2) The pH of the above solution was adjusted to neutral (pH 7) using a 30% sodium hydroxide aqueous solution to obtain the aqueous phase;

[0033] (3) Mix 13.5 g of styrene, 2.0 g of N-phenylmaleimide and 0.40 g of sorbitan monooleate (Span-80) evenly to obtain the oil phase;

[0034] (4) Under stirring conditions, the oil phase is slowly added to the aqueous phase by dropwise addition, and emulsified for 20 min at an emulsifier speed of 4000 rpm to obtain a pre-emulsion;

[0035] (5) Dissolve 0.12 g of potassium persulfate in 5.0 g of deionized water to prepare an initiator aqueous solution; transfer the pre-emulsion to a three-necked flask, purge with nitrogen for 20 min to remove oxygen, raise the temperature to 70 ℃, and after the temperature stabilizes, add the initiator aqueous solution dropwise under stirring to initiate the emulsion polymerization reaction. After the addition is complete, stir the reaction at 70 ℃ for 6 h. After the reaction is completed, cool to room temperature, filter and centrifuge to remove a small amount of gel and insoluble matter, and obtain the target flexible sealing agent emulsion.

[0036] Figure 1 This is the infrared spectrum of the sealing agent emulsion prepared in this embodiment after freeze-drying. Figure 1 It can be known that at 3441 cm -1A broad absorption peak appears nearby, which can be attributed to the NH stretching vibration in the amide group and the OH stretching vibration in the adsorbed water; at 3058 cm⁻¹ -1 and 3023 cm -1 The absorption peaks appearing nearby can be attributed to the stretching vibration of the aromatic ring CH; at 2917 cm⁻¹ -1 and 2847 cm -1 The absorption peaks appearing nearby can be attributed to the stretching vibrations of aliphatic CH4; at 1772 cm⁻¹ -1 and 1711 cm -1 The presence of a characteristic absorption peak nearby can be attributed to the characteristic vibration of C=O in the imide group, indicating the introduction of the structural unit corresponding to N-phenylmaleimide into the product; at 1658 cm⁻¹ -1 The absorption peaks appearing nearby can be attributed to the C=O related vibrations of the amide group; at 1601 cm⁻¹ -1 The absorption peaks appearing nearby can be attributed to the skeletal vibrations of the benzene ring; at 1491 cm⁻¹ -1 The nearby absorption peak can be attributed to the deformation vibrations of the methyl or methylene groups in the MPC structural unit; at 1191 cm⁻¹ -1 1042 cm -1 and 967 cm -1 The absorption peaks appearing nearby can be attributed to vibrations related to sulfonic acid and phosphorylcholine groups; at 755 cm⁻¹ -1 and 694 cm -1 The presence of absorption peaks nearby can be attributed to the out-of-plane bending vibration of the CH group in the benzene ring. Based on the composition of the raw materials and the attribution of the aforementioned characteristic absorption peaks, the target product has been successfully prepared.

[0037] Figure 2 This is a thermal stability analysis chart of the sealing agent emulsion prepared in this embodiment after freeze-drying. Figure 2 It can be seen that the plugging agent exhibits a phased weight loss characteristic during the heating process: when the temperature rises to 220℃, the weight loss is 4.3%; when the temperature rises from 220℃ to 350℃, a further weight loss of 18.5% occurs; when the temperature rises from 350℃ to 463℃, the weight loss is 66.6%, which is the main thermal decomposition stage of the sample; after 463℃, the thermogravimetric curve gradually flattens out. This indicates that the plugging agent has good thermal stability below 220℃ and can still maintain a certain residual structure at higher temperatures, indicating that the emulsion plugging agent of this invention has good heat resistance.

[0038] Figure 3 This is a particle size distribution diagram of the plugging agent emulsion prepared in this embodiment, from... Figure 3It is known that the Dx(50) of the emulsion plugging agent is 265 nm at room temperature, and the particle size distribution exhibits a single-peak characteristic, with the distribution peak located around 270 to 300 nm. The particle size of the emulsion plugging agent is mainly distributed in the range of 100 to 800 nm, with a more concentrated distribution in the range of 150 to 600 nm. This indicates that the obtained emulsion plugging agent particles are generally at the nanoscale and have a relatively continuous particle size distribution characteristic, which is beneficial for its plugging effect in formation pores or microfractures.

[0039] Figure 4 This is an appearance diagram of the sealing agent emulsion prepared in this embodiment.

[0040] Example 2

[0041] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluids includes the following steps:

[0042] (1) Add 2.0 g of octylphenol polyoxyethylene ether (OP-10) to 65.0 g of deionized water and stir at room temperature until completely dissolved; add 8.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 3.0 g of sodium p-styrenesulfonate, 3.5 g of 2-methacryloyloxyethyl phosphorylcholine and 0.06 g of crosslinking agent N,N′-methylenebisacrylamide in sequence, and continue stirring to obtain a homogeneous solution;

[0043] (2) The pH of the above solution was adjusted to neutral (pH 7) using a 30% sodium hydroxide aqueous solution to obtain the aqueous phase;

[0044] (3) Mix 13.5 g of styrene, 2.0 g of N-phenylmaleimide and 0.40 g of sorbitan monooleate (Span-80) evenly to obtain the oil phase;

[0045] (4) Under stirring conditions, the oil phase is slowly added to the aqueous phase by dropwise addition, and emulsified for 20 min at an emulsifier speed of 4000 rpm to obtain a pre-emulsion;

[0046] (5) Dissolve 0.12 g of potassium persulfate in 5.0 g of deionized water to prepare an initiator aqueous solution; transfer the pre-emulsion to a three-necked flask, purge with nitrogen for 20 min to remove oxygen, raise the temperature to 70 ℃, and after the temperature stabilizes, add the initiator aqueous solution dropwise under stirring to initiate the emulsion polymerization reaction. After the addition is complete, stir the reaction at 70 ℃ for 6 h. After the reaction is completed, cool to room temperature, filter and centrifuge to remove a small amount of gel and insoluble matter, and obtain the target flexible sealing agent emulsion.

[0047] Example 3

[0048] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluids includes the following steps:

[0049] (1) Add 2.0 g of octylphenol polyoxyethylene ether (OP-10) to 65.0 g of deionized water and stir at room temperature until completely dissolved; add 6.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 5.0 g of sodium p-styrenesulfonate, 3.5 g of 2-methacryloyloxyethyl phosphorylcholine and 0.06 g of crosslinking agent N,N′-methylenebisacrylamide in sequence, and continue stirring to obtain a homogeneous solution;

[0050] (2) The pH of the above solution was adjusted to neutral (pH 7) using a 30% sodium hydroxide aqueous solution to obtain the aqueous phase;

[0051] (3) Mix 13.5 g of styrene, 2.0 g of N-phenylmaleimide and 0.40 g of sorbitan monooleate (Span-80) evenly to obtain the oil phase;

[0052] (4) Under stirring conditions, the oil phase is slowly added to the aqueous phase by dropwise addition, and emulsified for 20 min at an emulsifier speed of 4000 rpm to obtain a pre-emulsion;

[0053] (5) Dissolve 0.12 g of potassium persulfate in 5.0 g of deionized water to prepare an initiator aqueous solution; transfer the pre-emulsion to a three-necked flask, purge with nitrogen for 20 min to remove oxygen, raise the temperature to 70 ℃, and after the temperature stabilizes, add the initiator aqueous solution dropwise under stirring to initiate the emulsion polymerization reaction. After the addition is complete, stir the reaction at 70 ℃ for 6 h. After the reaction is completed, cool to room temperature, filter and centrifuge to remove a small amount of gel and insoluble matter, and obtain the target flexible sealing agent emulsion.

[0054] Example 4

[0055] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluids includes the following steps:

[0056] (1) Add 1.0 g of octylphenol polyoxyethylene ether (OP-10) to 55.0 g of deionized water and stir at room temperature until completely dissolved; add 7.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 4.0 g of sodium p-styrenesulfonate, 2 g of 2-methacryloyloxyethyl phosphorylcholine and 0.04 g of crosslinking agent N,N′-methylenebisacrylamide in sequence, and continue stirring to obtain a homogeneous solution;

[0057] (2) The pH of the above solution was adjusted to neutral (pH 7) using a 30% sodium hydroxide aqueous solution to obtain the aqueous phase;

[0058] (3) Mix 12g of styrene, 1g of N-phenylmaleimide and 0.20g of sorbitan monooleate (Span-80) evenly to obtain the oil phase;

[0059] (4) Under stirring conditions, the oil phase is slowly added to the aqueous phase by dropwise addition, and emulsified for 20 min at an emulsifier speed of 4000 rpm to obtain a pre-emulsion;

[0060] (5) Dissolve 0.1 g of potassium persulfate in 5.0 g of deionized water to prepare an initiator aqueous solution; transfer the pre-emulsion to a three-necked flask, purge with nitrogen for 20 min to remove oxygen, raise the temperature to 70 ℃, and after the temperature stabilizes, add the initiator aqueous solution dropwise under stirring to initiate the emulsion polymerization reaction. After the addition is complete, stir the reaction at 70 ℃ for 4 h. After the reaction is completed, cool to room temperature, filter and centrifuge to remove a small amount of gel and insoluble matter, and obtain the target flexible sealing agent emulsion.

[0061] Example 5

[0062] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluids includes the following steps:

[0063] (1) Add 3.0 g of octylphenol polyoxyethylene ether (OP-10) to 75.0 g of deionized water and stir at room temperature until completely dissolved; add 7.0 g of 2-acrylamido-2-methylpropanesulfonic acid, 4.0 g of sodium p-styrenesulfonate, 5 g of 2-methacryloyloxyethyl phosphorylcholine and 0.08 g of crosslinking agent N,N′-methylenebisacrylamide in sequence, and continue stirring to obtain a homogeneous solution;

[0064] (2) The pH of the above solution was adjusted to neutral (pH 7) using a 30% sodium hydroxide aqueous solution to obtain the aqueous phase;

[0065] (3) Mix 16g of styrene, 4g of N-phenylmaleimide and 0.60g of sorbitan monooleate (Span-80) evenly to obtain the oil phase;

[0066] (4) Under stirring conditions, the oil phase is slowly added to the aqueous phase by dropwise addition, and emulsified for 20 min at an emulsifier speed of 4000 rpm to obtain a pre-emulsion;

[0067] (5) Dissolve 0.2 g of potassium persulfate in 5.0 g of deionized water to prepare an initiator aqueous solution; transfer the pre-emulsion to a three-necked flask, purge with nitrogen for 20 min to remove oxygen, then heat to 75 ℃. After the temperature stabilizes, add the initiator aqueous solution dropwise under stirring to initiate the emulsion polymerization reaction. After the addition is complete, stir the reaction at 75 ℃ for 6 h. After the reaction is completed, cool to room temperature, filter and centrifuge to remove a small amount of gel and insoluble matter, and obtain the target flexible sealing agent emulsion.

[0068] Comparative Example 1

[0069] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that the amount of 2-acrylamido-2-methylpropanesulfonic acid is 4.0 g, and the amount of other monomers and other steps and conditions are the same as in Example 1.

[0070] Comparative Example 2

[0071] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that the amount of sodium styrene sulfonate used is 2.0 g, while the amount of other monomers and other steps and conditions are the same as in Example 1.

[0072] Comparative Example 3

[0073] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that the amount of 2-methacryloyloxyethylphosphorylcholine is 6.0 g, and the amounts of other monomers and other steps and conditions are the same as in Example 1.

[0074] Comparative Example 4

[0075] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that the amount of styrene used is 22.0 g, and the amount of other monomers and other steps and conditions are the same as in Example 1.

[0076] Comparative Example 5

[0077] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is provided, following the preparation method of Example 1, except that the crosslinking agent N,N′-methylenebisacrylamide is not added. Other steps and conditions are the same as in Example 1.

[0078] Comparative Example 6

[0079] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that the amount of N-phenylmaleimide is 6.0g, and the amount of other monomers and other steps and conditions are the same as in Example 1.

[0080] Comparative Example 7

[0081] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that styrene is not added; other steps and conditions are the same as in Example 1.

[0082] Comparative Example 8

[0083] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that N-phenylmaleimide is not added; other steps and conditions are the same as in Example 1.

[0084] Comparative Example 9

[0085] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that 2-methacryloyloxyethylphosphorylcholine is not added; other steps and conditions are the same as in Example 1.

[0086] Comparative Example 10

[0087] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate are not added; other steps and conditions are the same as in Example 1.

[0088] Comparative Example 11

[0089] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that N-phenylmaleimide is replaced with N-methylmaleimide; other steps and conditions are the same as in Example 1.

[0090] Comparative Example 12

[0091] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that: octylphenol polyoxyethylene ether (OP-10) is replaced with fatty alcohol polyoxyethylene ether (AEO-9); other steps and conditions are the same as in Example 1.

[0092] Comparative Example 13

[0093] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that: sorbitan monooleate (Span-80) is replaced with sorbitan anhydride monostearate (Span-60); other steps and conditions are the same as in Example 1.

[0094] Comparative Example 14

[0095] A method for preparing a low-density flexible plugging agent for marine oil and gas drilling fluid is carried out according to the preparation method of Example 1, except that 2-methacryloyloxyethyl phosphorylcholine is replaced with 3-[2-(methacryloyloxy)ethyl]dimethylammonium propane-1-sulfonic acid inner salt; other steps and conditions are the same as in Example 1.

[0096] Experimental Example 1

[0097] First, prepare a 4% drilling fluid-based slurry: Add 400 g of sodium-based bentonite and 14 g of sodium carbonate to 10,000 mL of deionized water, stir at high speed for 20 min, and then seal and cure at room temperature for 24 h to obtain a 4% drilling fluid-based slurry.

[0098] Performance evaluation was conducted according to the national standard GB / T29170-2012, "Laboratory Testing of Drilling Fluids for Petroleum and Natural Gas Industry". Using the aforementioned 4% drilling fluid base slurry as a blank control, the samples from the examples and comparative examples were added at 3.0 wt% of the total base slurry mass and fully dispersed. The rheological parameters and filtration loss at room temperature and pressure were then measured. Subsequently, the samples were aged according to the aforementioned standard, and their filtration loss at high temperature and pressure was measured again after aging. The test results for each group are summarized in Table 1.

[0099] Table 1. Rheological filtration test of the base slurry with added examples and comparative samples.

[0100]

[0101] As shown in Table 1, after adding the plugging agent of the present invention to the base slurry at 3.0 wt% of the total mass of the base slurry, the rheological parameters of each system were improved compared with the blank base slurry. The filtration loss at room temperature and pressure and the filtration loss at high temperature and pressure after aging at 200 ℃ / 16 h were significantly reduced, indicating that the plugging agent of the present invention can improve the rheological properties and filtration loss control performance of the drilling fluid system. Among them, Example 1 has better overall performance, with the filtration loss at room temperature and pressure decreasing from 28 mL in the blank base slurry to 10 mL, and the filtration loss at high temperature and pressure after aging at 200 ℃ / 16 h decreasing from 168 mL to 55 mL. The filtration losses at high temperature and pressure after aging in Examples 2 to 5 were 67 mL, 68 mL, 75 mL and 71 mL, respectively, all lower than the blank base slurry, indicating that the plugging agent of the present invention still has good filtration loss control ability and system stability under high temperature aging conditions. The results show that the sulfonic acid and amide groups in 2-acrylamido-2-methylpropanesulfonic acid are beneficial to improving the hydration and dispersion capabilities and rheological retention of the system. The sodium sulfonate group and benzene ring structure in sodium styrenesulfonate are beneficial to improving the dispersion stability and the density of the plugging layer. The phosphorylcholine group in 2-methacryloyloxyethyl phosphorylcholine is beneficial to improving the hydration stability and salt environment adaptability of the system. The aromatic rigid structure in styrene and N-phenylmaleimide is beneficial to maintaining the stability of the copolymer skeleton. The crosslinking network formed by N,N′-methylenebisacrylamide is beneficial to improving the integrity of the plugging layer under high-temperature conditions. The synergistic effect of the above functional groups and crosslinking structures enables the obtained plugging agent to achieve both rheological regulation and filtration loss reduction under high-temperature aging conditions.

[0102] Experimental Example 2

[0103] Using the 4% drilling fluid-based slurry described in Example 1 as a blank control, the samples from the examples and comparative examples were added at 3.0 wt% of the total slurry mass and fully dispersed. After hot rolling at 200℃ for 16 hours, test samples were obtained. A sand bed was constructed using 110-160 mesh quartz sand to simulate the formation pore / throat structure. The sealing ability of the test samples on the sand bed was evaluated under medium pressure differential (0.7 MPa). The experimental results are shown in Table 2.

[0104] Table 2. Medium-pressure sand bed sealing experiment

[0105]

[0106] Table 2 shows that the blank base slurry experienced total leakage under medium-pressure sand bed conditions after hot rolling at 200℃ for 16 h. After adding the sealing agent of this invention, the penetration depth into the sand bed of each sample significantly decreased, indicating that the prepared sealing agent still possesses good sand bed sealing ability and high-temperature stability after high-temperature aging. Specifically, Example 1 showed a sand bed penetration depth of 3.5 cm, demonstrating superior sealing effect; Examples 2 to 5 showed penetration depths of 4.2 cm, 4.6 cm, 6.8 cm, and 5.5 cm, respectively, all significantly less than the blank base slurry. Comparative Examples 1 to 6 showed generally higher penetration depths than the examples, indicating that the components and their proportions in this invention are beneficial for improving the sealing ability of the sealing agent after high-temperature aging.

[0107] Experimental Example 3

[0108] Using pure water as a blank control, the samples from the examples and comparative examples were added at 3.0 wt% of the total mass of pure water and fully dispersed to obtain test samples. Microporous filter membranes with different pore sizes were used to simulate the nanoscale pore structure characteristics of rock samples. The filtration loss of the test samples was measured under normal temperature and pressure conditions to evaluate their blocking effect under different pore size conditions; the results are shown in Table 3.

[0109] Table 3 Filtration loss test of microporous membranes with different pore sizes

[0110]

[0111] Table 3 shows that pure water experienced total leakage under 100 nm, 200 nm, and 450 nm microporous membrane conditions. After adding the blocking agent of this invention, the filtration loss of each sample was significantly reduced. Specifically, the filtration losses of Example 1 under 100 nm, 200 nm, and 450 nm microporous membrane conditions were 65 mL, 60 mL, and 92 mL, respectively; and those of Example 2 were 72 mL, 68 mL, and 101 mL, respectively, all significantly lower than those of Comparative Example 1 (138 mL, 132 mL, and 148 mL) and Comparative Example 2 (130 mL, 126 mL, and 142 mL). Particularly under 200 nm microporous membrane conditions, the filtration losses of Examples 1 and 2 were relatively low, indicating that a closer match between the micropore size and the particle size of the blocking agent is more conducive to the formation of an effective blocking layer, thereby reducing filtration loss. These results demonstrate that the blocking agent of this invention has a good blocking effect on microporous channels of different sizes, with a better blocking effect on microporous channels whose particle size is matched.

[0112] Test Example 4

[0113] Rock samples with porous structure characteristics were selected as test objects, and eight groups of samples were set up: original rock sample, water-treated rock sample, rock sample treated in Example 1, rock sample treated in Example 2, rock sample treated in Example 3, rock sample treated in Comparative Example 1, rock sample treated in Comparative Example 2, and rock sample treated in Comparative Example 3.

[0114] Preparation of a treatment solution containing 3.0 wt% plugging agent: The plugging agent emulsion prepared in the examples or comparative examples is prepared by dispersing it in water, wherein the mass of the plugging agent emulsion prepared in the examples or comparative examples is 3 wt% of the mass of water.

[0115] Under a vacuum of 0.08 MPa, 10 g rock samples were immersed for 4 h in 350 mL of water, 350 mL of treatment solution containing 3.0 wt% of the plugging agent from Example 1, 350 mL of treatment solution containing 3.0 wt% of the plugging agent from Example 2, 350 mL of treatment solution containing 3.0 wt% of the plugging agent from Example 3, 350 mL of treatment solution containing 3.0 wt% of the plugging agent from Comparative Example 1, 350 mL of treatment solution containing 3.0 wt% of the plugging agent from Comparative Example 2, and 350 mL of treatment solution containing 3.0 wt% of the plugging agent from Comparative Example 3, respectively. The samples were then filtered and dried at 105 °C for 4 h to obtain the corresponding treated rock samples. Subsequently, the specific surface area and total pore volume of each group of samples were determined by gas adsorption method to evaluate the effect of different treatment systems on the pore structure of the rock samples. The results are shown in Table 4.

[0116] Table 4 Test results of the influence of each treatment system on the pore structure of rock samples

[0117]

[0118] As shown in Table 4, the specific surface area and pore volume of the rock sample after water treatment were 16.521 m². 2 ·g -1 and 0.0384cm 3 ·g -1 All are higher than the original rock sample's 6.415 m. 2 ·g -1 and 0.023 cm 3 ·g -1 After treatment with the sealing agent, the specific surface area and pore volume of the rock samples were significantly reduced. Specifically, the specific surface area and pore volume of the rock sample treated in Example 1 were 8.318 m². 2 ·g -1 and 0.027 cm 3 ·g -1 Example 2 is 8.742 m 2 ·g -1 and 0.0281 cm 3 ·g -1 Example 3 is 9.286 m 2 ·g -1 and 0.0293 cm 3 ·g -1 The specific surface areas of the rock samples treated with water were all lower than those treated with water; the specific surface areas of the rock samples treated with comparative examples 1 to 3 were 13.684 m², respectively. 2 ·g -1 12.458 m 2 ·g -1 and 11.367 m 2 ·g -1 The pore volumes are 0.0372 cm³. 3 ·g -1 0.0361 cm 3 ·g -1 and 0.0351 cm 3 ·g -1 The overall performance was higher than that of the Example 1 group. The above results indicate that the sealing agent of the present invention can penetrate the pores of the rock sample and seal them, thereby reducing the effective specific surface area and pore volume of the rock sample; among them, the rock sample treated in Example 1 had the lowest specific surface area and pore volume, indicating that its sealing effect was superior.

[0119] Experimental Example 5

[0120] Using the 4% drilling fluid base slurry described in Experimental Example 1 as a blank control, samples from Examples 1 to 5 and Comparative Examples 1 to 14 were added to the base slurry at 3.0 wt% of the total mass of the base slurry and fully dispersed. The rheological parameters and filtration loss of each system were measured at room temperature (25 ℃) and 4 ℃, where 4 ℃ was used to simulate the low temperature environment of the ocean seabed. The results are shown in Table 5.

[0121] Table 5. Rheological parameters and filtration loss of each sample at room temperature and 4 °C

[0122]

[0123] As shown in Table 5, after adding the plugging agent of the present invention, all systems exhibited good rheological properties and filtration loss control capabilities at both room temperature (25 ℃) and 4 ℃. Compared with room temperature, although AV, PV, and YP of Examples 1 to 5 increased at 4 ℃, the overall change was small, indicating that the plugging agent of the present invention can still maintain good rheological stability at low temperatures. Specifically, the AV, PV, and YP of Example 1 at 4 ℃ were 36.5 mPa·s, 21.5 mPa·s, and 15 Pa, respectively, showing only a slight increase compared to room temperature, with a low-temperature filtration loss of 7 mL. The low-temperature filtration losses of Examples 2 to 5 were 10 mL, 11 mL, 12 mL, and 8.5 mL, respectively, all significantly lower than those of the comparative examples. In contrast, the comparative sample showed a relatively large increase in AV, PV, and YP at 4 ℃, indicating weaker low-temperature rheological stability. The above results demonstrate that the plugging agent of the present invention can maintain the stability of the system's rheological parameters well at low temperatures and has a good low-temperature filtration loss control effect.

[0124] Experimental Example 6

[0125] Using the 4% drilling fluid base slurry described in Example 1 as a blank control, the plugging agents obtained from Examples 1, 9, 10, and 14 were added to the base slurry at 3.0 wt% of the total mass, and stirred to ensure thorough dispersion. Then, different masses of NaCl were added, and stirring continued until the system was homogeneous, thus preparing drilling fluid samples under different salt concentration conditions. The rheological parameters and filtration loss of each sample were measured at room temperature (25 ℃) to evaluate the performance retention of each plugging agent under salt contamination conditions. The test results are shown in Table 6.

[0126] Table 6. Rheological parameters and filtration loss test results of each system under different NaCl dosage conditions.

[0127]

[0128] As shown in Table 6, with the increase of NaCl dosage, the AV, PV, and YP of each system generally decreased, while the filtration loss generally increased, indicating that the rheological properties and filtration loss control performance of the drilling fluid system changed under salt contamination conditions. Compared with the base slurry, the rheological properties and filtration loss control performance of each system under different salt concentrations were improved after the addition of the plugging agent. Among them, Example 1 showed higher rheological parameters and lower filtration loss under all NaCl dosage conditions, and its overall performance was better than that of Comparative Examples 9, 10, and 14, indicating that the plugging agent obtained in Example 1 has better salt resistance.

Claims

1. A flexible plugging agent for marine oil and gas drilling fluid, characterized in that, It is prepared from the following parts by mass of raw materials: Styrene 12-16 parts, N-phenylmaleimide 1-4 parts, 2-acrylamido-2-methylpropanesulfonic acid 6-8 parts, sodium p-styrenesulfonate 3-5 parts, 2-methacryloyloxyethyl phosphorylcholine 2-5 parts, crosslinking agent 0.04-0.08 parts, initiator 0.1-0.2 parts, hydrophilic emulsifier 1-3 parts, lipophilic emulsifier 0.2-0.6 parts, water 60-80 parts; The hydrophilic emulsifier is octylphenol polyoxyethylene ether, and the lipophilic emulsifier is sorbitol monooleate.

2. The flexible plugging agent for marine oil and gas drilling fluid according to claim 1, characterized in that, The crosslinking agent is N,N′-methylenebisacrylamide.

3. The flexible plugging agent for marine oil and gas drilling fluid according to claim 1, characterized in that, The initiator is potassium persulfate.

4. The method for preparing the flexible plugging agent for marine oil and gas drilling fluid as described in any one of claims 1-3, characterized in that, Including the following steps: (1) Disperse the hydrophilic emulsifier fully in water, add 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, 2-methacryloyloxyethylphosphonic choline, and crosslinking agent, mix thoroughly, adjust pH, and obtain an aqueous phase; (2) Mix the lipophilic emulsifier, styrene, and N-phenylmaleimide evenly to obtain the oil phase; (3) Under stirring conditions, the oil phase is added dropwise to the aqueous phase and emulsified to obtain a pre-emulsion; an initiator aqueous solution is added dropwise, and after polymerization reaction and filtration, a flexible plugging agent for marine oil and gas drilling fluid is obtained.

5. The method for preparing the flexible plugging agent for marine oil and gas drilling fluid according to claim 4, characterized in that, In step (1), the pH is adjusted to 7 using a sodium hydroxide aqueous solution with a mass concentration of 20-40%.

6. The method for preparing the flexible plugging agent for marine oil and gas drilling fluid according to claim 4, characterized in that, In step (3), the emulsification speed is 3000-5000 rpm and the emulsification time is 10-30 min.

7. The method for preparing the flexible plugging agent for marine oil and gas drilling fluid according to claim 4, characterized in that, In step (3), the mass concentration of the initiator aqueous solution is 2%-3%.

8. The method for preparing the flexible plugging agent for marine oil and gas drilling fluid according to claim 4, characterized in that, In step (3), the polymerization reaction temperature is 70-75℃, the polymerization reaction time is 4-6h, and the polymerization reaction is carried out under a protective atmosphere and stirring conditions; the protective atmosphere is nitrogen.

9. The application of the flexible plugging agent for marine oil and gas drilling fluid as described in any one of claims 1-3 in marine oil and gas drilling fluid.

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